Flux lattice imaging of a patterned niobium thin film

Using our cryogenic magnetic force microscope, we have investigated a super conducting Nb thin film, 100 nm in thickness with T-c similar to 6.5 K. The film is patterned with a square array (1 mum x 1 mum) of antidots, which s erve as artificial pinning centers for magnetic flux. We have observed flux lattice matching as a function of applied magnetic field and temperature, for field strengths up to the third matching field, with evidence of flux d ragging by the tip around the antidots. Force gradient distance curves acqu ired at temperatures about T-c clearly demonstrate an observable Meissner f orce between tip and sample, and allow for an estimation of the magnetic sc reening penetration depth. (C) 2001 American Institute of Physics.